1. Field of the Invention
The present invention relates to an improvement of a permanent magnet type three-phase twelve-pole stepping motor that is employed in OA equipment such as a copier, a scanner g or the like.
2. Description of Prior Arts
A pitch of stator teeth of a conventional three-phase twelve-pole permanent magnet type stepping motor is equal to a pitch of rotor teeth, and three phases, which are U-phase, V-phase and W-phase, are spatially distributed at 120 degrees intervals. Further, since a hybrid type rotor has 180 degrees of phase difference among the magnet poles, a N-pole and a S-pole, the fourth harmonic component is erased in a space of a field magnet of an air gap among the phases.
In this case, although the fourth harmonic component forms a cogging torque in the space of the field magnet of the air gap, the cogging torque of the conventional three-phase hybrid type stepping motor becomes minimum according to the above-described effect.
Incidentally, in the above-described conventional construction, the fourth harmonic component included in the magnetic flux in the field magnet formed in the air gap takes small value when the pole pair number Nr of the rotor becomes large, because the phase between the N-pole and the S-pole formed on the rotor equals to (180/Nr) degrees in a mechanical angle. Accordingly, since a slight error of the mechanical angle results in a large error of the electrical angle, the fourth harmonic component of the field magnet formed among the phases cannot be erased.
Therefore, the values of the cogging torque vary and there may be a product having a part of large cogging torque, which results the variation in an oscillation noise. Further, the effect of the harmonic components is the same when the second harmonic component, the third harmonic component and the fifth harmonic component exist, and therefore, these harmonic components are required to be removed.
An object of the present invention is to provide a permanent magnet type twelve-pole stepping motor that eliminates the defects mentioned above.
A permanent magnet type twelve-pole stepping motor of an inner rotor type described in claim 1 comprises,
a stator comprising a yoke portion having approximately annular shape, a stator iron-core made from magnetic material having twelve stator main poles that are directed from the inner circumferential surface of the yoke portion toward the center and each having a plurality of small teeth on the tip end thereof, and stator coils wound in the stator iron-core;
a so-called hybrid type rotor, which is rotatably supported by the stator through a predetermined air gap, having a cylindrical permanent magnet magnetized in a rotation axis direction that is sandwiched between a pair of rotors made from magnetic material each having Nr pieces of pole teeth around the outer circumferential surface thereof at equal pitch and the rotors being arranged such that the pole teeth are deviated with each other, or a permanent magnet type rotor whose cylindrical outer circumferential surface is magnetized in a direction parallel to the rotation axis to form Nr pairs of N-pole and S-pole alternately;
wherein said stator is formed as three-phase winding and second harmonic component, third harmonic component, fourth harmonic component and fifth harmonic component are removed by composing cogging torque of the respective phases by means of the three-phase twelve-pole construction, further any one harmonic component of the cogging torque among the second harmonic component, the third harmonic component, the fourth harmonic component and the fifth harmonic component is independently erased by making a difference between the small teeth pitch of said stator main pole and the rotor teeth pitch or the pole pair number pitch, thereby any one harmonic component among the second harmonic component, the third harmonic component, the fourth harmonic component and the fifth harmonic component is doubly erased.
Further, a permanent magnet type twelve-pole stepping motor of an outer rotor type described in claim 2 comprises,
a stator comprising a yoke portion having approximately annular shape, a stator iron-core made from magnetic material having twelve stator main poles that are formed on the outer circumferential surface of the yoke portion aligned radially and each having a plurality of small teeth on the tip end thereof, and stator coils wound in the stator iron-core;
a so-called hybrid type rotor, which is rotatably supported by the stator through a predetermined air gap, having a cylindrical permanent magnet magnetized in a rotation axis direction that is sandwiched between a pair of rotors made from magnetic material each having Nr pieces of pole teeth around the inner circumferential surface thereof at equal pitch and the rotors being arranged such that the pole teeth are deviated with each other, or a permanent magnet type rotor whose cylindrical inner circumferential surface is magnetized in a direction parallel to the rotation axis to form Nr pairs of N-pole and S-pole alternately;
wherein said stator is formed as three-phase winding and second harmonic component, third harmonic component, fourth harmonic component and fifth harmonic component are removed by composing cogging torque of the respective phases by means of the three-phase twelve-pole construction, further any one harmonic component of the cogging torque among the second harmonic component, the third harmonic component, the fourth harmonic component and the fifth harmonic component is independently erased by making a difference between the small teeth pitch of said stator main pole and the rotor teeth pitch or the pole pair number pitch, thereby any one harmonic component among the second harmonic component, the third harmonic component, the fourth harmonic component and the fifth harmonic component is doubly erased.
Further, a permanent magnet type twelve-pole stepping motor of an inner rotor type described in claim 3 comprises,
a stator comprising a yoke portion having approximately annular shape, a stator iron-core made from magnetic material having twelve stator main poles that are directed from the inner circumferential surface of the yoke portion toward the center and each having a plurality of small teeth on the tip end thereof, and stator coils wound in the stator iron-core;
a so-called hybrid type rotor, which is rotatably supported by the stator through a predetermined air gap, having a cylindrical permanent magnet magnetized in a rotation axis direction that is sandwiched between a pair of rotors made from magnetic material each having Nr pieces of pole teeth around the outer circumferential surface thereof at equal pitch and the rotors being arranged such that the pole teeth are deviated with each other, or a permanent magnet type rotor whose cylindrical outer circumferential surface is magnetized in a direction parallel to the rotation axis to form Nr pairs of N-pole and S-pole alternately;
wherein said stator is formed as three-phase winding and second harmonic component, third harmonic component, fourth harmonic component and fifth harmonic component are removed by composing cogging torque of the respective phases by means of the three-phase twelve-pole construction, further any one harmonic component of the cogging torque among the component from the second harmonic to the third harmonic, the component from the third harmonic to the fourth harmonic and the component from the fourth harmonic to the fifth harmonic is independently erased by making a difference between the small teeth pitch of said stator main pole and the rotor teeth pitch or the pole pair number pitch.
Further, a permanent magnet type twelve-pole stepping motor of an outer rotor type described in claim 4 comprises,
a stator comprising a yoke portion having approximately annular shape, a stator iron-core made from magnetic material having twelve stator main poles that are formed on the outer circumferential surface of the yoke portion aligned radially and each having a plurality of small teeth on the tip end thereof, and stator coils wound in the stator iron-core;
a so-called hybrid type rotor, which is rotatably supported by the stator through a predetermined air gap, having a cylindrical permanent magnet magnetized in a rotation axis direction that is sandwiched between a pair of rotors made from magnetic material each having Nr pieces of pole teeth around the inner circumferential surface thereof at equal pitch and the rotors being arranged such that the pole teeth are deviated with each other, or a permanent magnet type rotor whose cylindrical inner circumferential surface is magnetized in a direction parallel to the rotation axis to form Nr pairs of N-pole and S-pole alternately;
wherein said stator is formed as three-phase winding and second harmonic component, third harmonic component, fourth harmonic component and fifth harmonic component are removed by composing cogging torque of the respective phases by means of the three-phase twelve-pole construction, further any one harmonic component of the cogging torque among the component from the second harmonic to the third harmonic, the component from the third harmonic to the fourth harmonic and the component from the fourth harmonic to the fifth harmonic is independently erased by making a difference between the small teeth pitch of said stator main pole and the rotor teeth pitch or the pole pair number pitch.
Further, a permanent magnet type twelve-pole stepping motor of an inner rotor type or an outer rotor type described in claim 5 is predicated on the claim 1 or 2 and is constructed so that the mechanical deviation angle (xcfx84) between the stator small teeth pitch and the rotor teeth pitch equals to (xcfx80/4Nr) radians to remove the second harmonic component when the number of the small teeth formed on each of the twelve stator main poles equals to four.
Further, a permanent magnet type twelve-pole stepping motor of an inner rotor type or an outer rotor type described in claim 6 is predicated on the claim 1 or 2 and is constructed so that the mechanical deviation angle (xcfx84) between the stator small teeth pitch and the rotor teeth pitch equals to (xcfx80/6Nr) radians to remove the third harmonic component when the number of the small teeth formed on each of the twelve stator main poles equals to four.
Further, a permanent magnet type twelve-pole stepping motor of an inner rotor type or an outer rotor type described in claim 7 is predicated on the claim 1 or 2 and is constructed so that the mechanical deviation angle (xcfx84) between the stator small teeth pitch and the rotor teeth pitch equals to (xcfx80/8Nr) radians to remove the fourth harmonic component when the number of the small teeth formed on each of the twelve stator main poles equals to four.
Further, a permanent magnet type twelve-pole stepping motor of an inner rotor type or an outer rotor type described in claim 8 is predicated on the claim 1 or 2 and is constructed so that the mechanical deviation angle (xcfx84) between the stator small teeth pitch and the rotor teeth pitch equals to (xcfx80/10Nr) radians to remove the fifth harmonic component when the number of the small teeth formed on each of the twelve stator main poles equals to four.
Still further, a permanent magnet type twelve-pole stepping motor of an inner rotor type or an outer rotor type described in claim 9 is predicated on the claim 1 or 2 and is constructed so that the mechanical deviation angle (xcfx84) between the stator small teeth pitch and the rotor teeth pitch ranges from (xcfx80/6Nr) to (xcfx80/4Nr) radians to remove the component from the second harmonic to the third harmonic, or ranges from (xcfx80/8Nr) to (xcfx80/6Nr) radians to remove the component from the third harmonic to the fourth harmonic, or ranges from (xcfx80/10Nr) to (xcfx80/8Nr) radians to remove the component from the fourth harmonic to the fifth harmonic when the number of the small teeth formed on each of the twelve stator main poles equals to four.
The construction as described in claim 1 or 2 allows removing the second harmonic component through the fifth harmonic component by means of the three-phase twelve-pole fundamental construction even if the phase between the pole teeth of the N-pole and the S-pole of the hybrid type rotor is out of order, and further, since any one harmonic component of the field magnet among the second harmonic component, the third harmonic component, the fourth harmonic component and the fifth harmonic component is erased at every stator phase with reliability, the respective harmonic components including the most influential fourth harmonic component as the main component can be erased with reliability, thereby a three-phase hybrid type stepping motor that is usually stable in a rotation characteristic and operates with low oscillation noise can be obtained.
Further, the construction as described in claim 3 or 4 allows removing the second harmonic component through the fifth harmonic component by means of the three-phase twelve-pole fundamental construction, and further, any one harmonic component of the field magnet among the second harmonic component, the third harmonic component, the fourth harmonic component and the fifth harmonic component is relieved at every stator phase.
Still further, the concrete actions of claims 5 through 9 will be described below, they show the functions to remove the second harmonic component through the fifth harmonic component when four small teeth are formed on the stator main pole.
This effect gives a similar effect to the three-phase permanent magnet type other than the hybrid and to the dimensional error of the permanent magnet magnetized on the rotor.
In general, the stator iron-core is manufactured by punching silicon steel plate with a punch press.
Since the phase difference between the magnetic pole formed on the rotor and the stator small teeth is almost determined by the accuracy of a stamping die, the motor that has high accuracy, low cogging torque and low variation can be obtained.
Accordingly, the oscillation and noise with rotation can be extensively reduced.